Communication signal equalization systems and methods

ABSTRACT

Communication signal equalization methods and systems are disclosed. A CDMA signal having a data portion and a known portion including a known or repeated data sequence and received over a multipath communication channel represents a linear convolution between the multipath channel and a transmitted CDMA signal. A channel estimate of the communication channel is determined from the known portion, and the CDMA signal is translated into a new CDMA signal which is a cyclic convolution with the channel estimate. A frequency domain representation of the new CDMA signal is adjusted using the channel estimate to produce a frequency domain representation of an equalized signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/493,331, filed on Aug. 8, 2003. The entirecontents of this provisional application are hereby incorporated hereinby reference.

FIELD OF THE INVENTION

The invention relates to communication signal equalization, and inparticular, to systems and methods for frequency domain equalization inCDMA (Code Division Multiple Access) systems.

BACKGROUND OF THE INVENTION

The IS2000 standard (release-A or 1xRTT) supports up to 153.6 kbps peakuser data rate, based on the CDG (CDMA Development Group) requirementsfor cdmaOne family evolution. One known so-called HDR (High Data Rate)system represents a major step forward to improve the packet data systemthroughput. A further improved version, HDR-1xEV-DO, has been adopted asan IS-856 standard, which aims to meet the CDG requirement for 1xRTT andevolution thereof. IS-856 is a data only system which will be overlaidon the 1xRTT network and uses a single carrier of 1.25 MHz co achieve asimilar data rate (2 Mbps) to a 3-carriers configuration of CDMA2000.Although the chip rate is same as in IS-95/1xRTT, i.e. 1.2288 Mcps,1xEV-DO introduces multiple enabling technologies. The basic 1xEV-DOemploys a multi-code of Walsh sequence to construct a fat data pipe.However, such a multi-code channel with low spreading factor suffersfrom orthogonality loss in the dispersive channel due to inter-codeinterference, i.e., inter-symbol interference.

There are several key differences between IS-856 and traditional CDMAsystems. For example, IS-856 is intended for non-real-time packet data.IS-856 is also a pure TDMA (Time Division Multiple Access) system,although signals are whitened by a scrambling code before transmission,occupies 1.25 MHz spectrum, and uses QPSK (Quadrature Phase ShiftKeying), 8-PSK and 16-QAM (Quadrature Amplitude Modulation) modulation,only turbo codes, and full power transmission. Rate adaptation with apeak race of 2.48 Mbps, mobility support, proportional fairnessscheduling, multi-user diversity, and connection with a PDSN (PacketData Serving Node) and then IP (Internet Protocol), and therefore noconnection with an MSC (Mobile Switching Center) or a circuit switchedcore network, represent further characteristics by which IS-856 differsfrom traditional CDMA systems.

The spectrum efficiency of IS-856 is achieved mainly by its TDMA signalstructure along with scrambling codes, which makes it possible forfrequency re-use one, fat-pipe scheduling to collect multi-userdiversity by closely tracking the Rayleigh fading channel, high ordermodulation, and use of turbo codes.

Similar to CDMA2000, the downlink physical channel of 1xEV-DO occupies a1.25 MHz spectrum with a chip rate 1.2288 Mcps. However, there is onlyone type of physical channel, which is divided into frames of 32768chips or 26.67 ms. Each frame is further divided into 16 slots each hasa length of 2048 chips or 1.67 ms. The slot is the basic unit and allother channels, such as the pilot channel, MAC (Media Access Control)channel, and traffic channels, will be multiplexed into a slot. In thedownlink transmission direction, slots are classified into two modes,including active and idle. In active mode, an access network has eithercontrol information or user traffic information to send along with thepilot and MAC channels multiplexed into that slot. In idle mode, theaccess network transmits only the pilot and MAC channels. Each half slothas 96 pilot chips and 2*64 MAC chips. In summary, the pilot channelutilizes 9.375% of bandwidth and the MAC channel occupies 12.5%bandwidth.

One current 1xEV-DO terminal receiver chip solution is based on the rakereceiver structure. The rake receiver works quite well in multi-pathenvironments when the spreading factor is larger than 16. However, inorder to increase the data throughput, 1xEV-DO employs a multi-codedownlink with spreading factor 16. In this case, the rake receiver-based1xEV/DO receiver has several limitations for implementation high levelmodulations. First, the baseband filter used at a transmitter is thesame as in CDMA2000/IS-95, i.e. a 48-tap (chip) non-Nyquist filter,which always causes ICI (inter-chip interference). In addition, themaximum number of rake receiver fingers is 4, which sets a CIR (Carrierto Interference Ratio) ceiling of 17.8 dB. The relatively small bitwidth per sample further limits receiver performance.

All of these limitations may dramatically degrade the system performancewhen the multipath environment is rich, such as in a dense urbanenvironment. The low sampling rate also causes finger detectioninaccuracy. When the speed of a mobile communication device is high,tracking of channel variation may also be difficult. In practice, highlevel modulation such as 16-QAM cannot be used due to ICI caused bynon-Nyquist filtering, and the 1xEV-DO high throughput is therebygenerally limited to that achieved by Turbo coding and fast scheduling.

SUMMARY OF THE INVENTION

Embodiments of the present invention address issues associated with1xEV-DO terminals and provide a simple frequency domain equalizer whichachieves performance close to OFDM (Orthogonal Frequency DivisionMultiplexing) systems. Equalizers according to embodiments of theinvention can mitigate performance loss for rake receiver-based 1xEV-DOterminals, allow the system to use even higher-level modulation such as64-QAM, and reduce receiver complexity by replacing rake receiverstructure with an FFT (Fast Fourier Transform) engine.

Downlink throughput may thus be enhanced by providing a frequency domainequalizer in a terminal receiver to alleviate ICI issues caused by bothmulti-path interference and non-Nyquist filtering, which prevents theuse of high-level modulation.

According to one aspect, the invention provides a method of equalizing aCDMA signal received over a multipath communication channel, the CDMAsignal having a data portion and a known portion which includes a knownor repeated data sequence and representing a linear convolution betweenthe multipath channel and a transmitted CDMA signal. The method involvesdetermining from the known portion a channel estimate of thecommunication channel, translating the CDMA signal into a new CDMAsignal which is a cyclic convolution with the channel estimate, andadjusting a frequency domain representation of the new CDMA signal usingthe channel estimate co produce a frequency domain representation of anequalized signal.

The operation of determining may include determining a time domainchannel estimate from the known portion. In this case, adjusting mayinvolve performing a time domain to frequency domain conversion on thetime domain channel estimate to produce a frequency domain channelestimate and adjusting the frequency domain representation of the newCDMA signal using the frequency domain channel estimate.

In some embodiments, translating involves subtracting the known portionfrom the CDMA signal to produce the new CDMA signal, replacing at leastsome of the known portion with a new portion which converts the CDMAsignal to the new CMDA signal.

A frequency domain to time domain conversion may be performed on thefrequency domain representation of the equalized signal to produce atime domain equalized signal.

According to one embodiment, adjusting involves performing acomponent-wise division of the frequency domain representation of thenew CDMA signal by the frequency domain channel estimate. Thecomponent-wise division may be performed for all values of the frequencydomain channel estimate or only for values of the frequency domainchannel estimate which are sufficiently large so as reduce effects ofamplifying noise components of the CDMA signal. In the latter case,components of the frequency domain representation of the new CDMA signalfor which the corresponding components of the frequency domain channelestimate are not sufficiently large may be replaced with a predeterminedvalue or weighted.

A communication signal processing method is also provided, and includesmultiplexing a data portion and a known portion which includes a knownor repeated data sequence into a CDMA signal and outputting the CDMAsignal for transmission to a receiver over a multipath communicationchannel and equalization at the receiver by determining from the knownportion a channel estimate of the communication channel, translating theCDMA signal into a new CDMA signal which is a cyclic convolution withthe channel estimate, and adjusting a frequency domain representation ofthe new CDMA signal using the channel estimate to produce a frequencydomain representation of an equalized signal.

In a further aspect of the invention, there is provided a system forequalizing a portion of a CDMA signal received over a multipathcommunication channel, the CDMA signal having a data portion and a knownportion which includes a known or repeated data sequence andrepresenting a linear convolution between the multipath channel and atransmitted CDMA signal. The system includes an input and a processorwhich is configured to receive the CDMA signal from the input, todetermine from the known portion a channel estimate of the communicationchannel, to translate the CDMA signal into a new CDMA signal which is acyclic convolution with the channel estimate, and to adjust a frequencydomain representation of the new CDMA signal using the channel estimateto produce a frequency domain representation of an equalized signal. Theprocessor may be further configured to perform these functions in aparticular manner or to perform additional functions.

A communication signal processing system at a transmitter is alsoprovided, and includes an input for receiving data to be transmitted,and a processor configured to receive the data from the input, tomultiplex the data and a known or repeated data sequence into a CDMAsignal to form a data portion and a known portion, and to output theCDMA signal for transmission to a receiver over a multipathcommunication channel and equalization at the receiver by determiningfrom the known portion a channel estimate of the communication channel,translating the CDMA signal into a new CDMA signal which is a cyclicconvolution with the channel estimate, and adjusting a frequency domainrepresentation of the new CDMA signal using the channel estimate toproduce a frequency domain representation of an equalized signal.

Yet another aspect of the invention provides a CDMA communication systemincluding communication equipment having a processor configured toreceive from an input data to be transmitted, to multiplex the data anda known or repeated data sequence into a CDMA signal co form a dataportion and a known portion, and to output the CDMA signal fortransmission, and communication equipment having a processor configuredto receive the CDMA signal over a multipath communication channel, todetermine from the known portion a channel estimate of the communicationchannel, to translate the CDMA signal into a new CDMA signal which is acyclic convolution with the channel estimate, and to adjust a frequencydomain representation of the new CDMA signal using the channel estimateto produce a frequency domain representation of an equalized signal.These types of communication equipment may be implemented at a networkelement of the communication system, a communication terminal adaptedfor operation in the communication system, or both.

Other aspects and features of embodiments of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific illustrative embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the invention will now be described ingreater detail with reference to the accompanying drawings, in which:

FIGS. 1A and 1B show a block diagram of a transmit chain for a 1xEV-DOforward communication link;

FIG. 2 is a plot of a filter response of a baseband filter of thetransmit chain of FIG. 1;

FIG. 3 is a block diagram illustrating a 1xEV-DO frame and slotstructure;

FIG. 4 is a block diagram of the slot structure of FIG. 3 illustratingdata which is buffered in accordance with an embodiment of theinvention, as an implementation example;

FIG. 5 is a flow diagram of a method according to an embodiment of theinvention;

FIG. 6, as an example, is a representation of received data for use inchannel estimation according to an embodiment of the invention; and

FIG. 7 is a block diagram of a system in which embodiments of theinvention may be implemented.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A and 1B show a block diagram of a transmit chain for a 1xEV-DOforward communication link. Those skilled in the art will appreciatethat the elements shown in FIGS. 1A and 1B represent an illustrativeexample of a transmit chain, and that the invention is in no way limitedto implementation in conjunction with a transmitter having the structureexplicitly shown in FIGS. 1A and 1B. Thus, the contents of FIGS. 1A and1B, as well as the other Figures described herein, are intended solelyfor illustrative purposes and do not limit the scope of the invention.

The transmit chain of FIGS. 1A and 1B, which would be implemented at abase station or other network element in a communication network for aforward link, includes signal paths for traffic or control channels, aMAC channel, and a pilot channel.

The traffic or control channel signal path includes an encoder 10,illustratively a coding rate R=1/3 or R=1/5 Turbo encoder, connected toa combiner 12 which is also connected to a scrambler 14 and a channelinterleaver 16. The channel interleaver 18 is connected to a sequencerepetition and symbol puncturing element 20, and the traffic/controlchannel transmit signal path continues with a symbol demultiplexer 22, aWalsh coding element 24, a Walsh channel gain element 26, and a Walshchip level summer 28.

The MAC channel path in FIGS. 1A and 1B includes a preamble path whichincludes a signal point mapping element 30, a multiplier 31, and asequence repetition element 32, a MAC RPC (Reverse Power Control) pathwhich includes a signal point mapping element 34, an RPC Walsh channelgain element 36, and a multiplier 38, and a MAC RA (Reverse Activity)path which includes a bit repetition element 44 with a repetition factorof a number of RA bits (RABLength), a signal point mapping element 46,an RA channel gain element 48, and a multiplier 50. The RPC and RA bitsoutput by the multipliers 38 and 50 are combined in the Walsh chip levelsummer 40, which is connected to a sequence repetition element 42 havinga repetition factor of 1.

In the pilot channel signal path, a signal point mapping element 52 isconnected to a multiplier 54.

All of the above signal paths are connected to the time divisionmultiplexer (TDM) 56, which outputs a multiplexed signal to thespreading element 58. Baseband filters 60 and 62 are connected to thespreading element 58 and output filtered signals to the multipliers 64,66. The baseband filters 60 and 62 of FIG. 1 are typically non-Nyquistfilters, and may have a response as shown in FIG. 2, for example. Thecombiner 68 combines modulated signals output from the multipliers 64,66 and outputs a modulated waveform, to an antenna or other transmittercomponents for transmission, for example.

The transmit chain of FIGS. 1A and 1B operates to generate a signalhaving a structure as shown in FIG. 3, which is a block diagramillustrating a 1xEV-DO frame and slot structure. Operation of thetransmit chain of FIGS. 1A and 1B will be apparent to those skilled inthe art and therefore is not described in detail herein.

As described briefly above, the downlink physical channel of 1xEV-DOoccupies a 1.25 MHz spectrum with a chip rate 1.2288 Mcps, and thephysical channel is divided into frames 70, 72 of 32768 chips or 26.67ms. Each frame 70, 72 is further divided into 16 slots of 2048 chips or1.67 ms in length. The traffic, control, pilot, and MAC channels aremultiplexed into a slot. The slot shown in FIG. 2 includes 400 chips ofcontrol or traffic data at 74, followed by 64 MAC chips 76, 96 pilotchips 78, another block of 64 MAC chips 80, and another block of 400control or traffic chips 82. This pattern is repeated at 84, 86, 88, 90,92. Thus, each half slot has 96 pilot chips, 2*64 MAC chips, and 800control or traffic chips.

Embodiments of the invention address various performance issuesassociated with 1xEV-DO terminal implementations using frequency domainequalization. In some embodiments, a multipath channel is conversed intoa single path in the frequency domain, similar to OFDM. However, it iswell known that OFDM systems translate a signal into a periodic signalby using the so-called Identical Cyclic Prefix so that the advantages ofa cyclic convolution are realized. In CDMA technology, the OFDMassumption of a cyclic prefix never holds, as a CDMA signal is alwaysscrambled by a PN sequence. The proposed frequency domain equalizer doesnot require such an assumption.

Downlink throughput is enhanced by providing a frequency domainequalizer to mitigate the multi-path distortion problem and thenon-Nyquist filter problem which cause ICI and prevent the use ofhigh-level modulation.

A frequency domain equalizer according to one embodiment exploits thedownlink slot structure to remove the multipath in the frequency domain,and equalized frequency domain data is converted to the time domain,using an IFFT (Inverse Fast Fourier Transform), for example. Althoughdetailed examples provided herein are applicable to 1xEV-DO, thestandard for which is hereby incorporated by reference in its entirety,it is to be understood that applications of the invention are notlimited to the context of this standard.

FIG. 4 is a block diagram of the slot structure of FIG. 3 illustratingdata which is buffered in accordance with one embodiment of theinvention. As chose skilled in the art will appreciate, a receivingterminal performs operations such as acquiring the system, includingframe timing and slot timing, in order to properly detect the slotstructure of FIG. 4. Therefore, a receiving terminal may perform theseoperations prior to or substantially concurrently with the equalizationoperations described in detail herein. Further operations may also beperformed prior to, concurrently with, or after equalization withoutdeparting from the scope of the invention.

In the illustrated embodiment, a slot includes 400 chips of control ortraffic data 100, a block of 64 MAC chips 102, 96 pilot chips 104,another block of 64 MAC chips 106, another block of 400 chips of controlor traffic data 108, and a similar pattern of 400 control or trafficchips 110, 64 MAC chips 112, 96 pilot chips 114, 64 MAC chips 116, and400 control or traffic chips 118, of which 1024 chips are buffered, in aFIFO (First In First Out) register in a memory device, for example, forprocessing. The buffered data includes a control or traffic data portion108, 110 between two adjacent pilot portions 104, 114. The buffer sizeand timers are thus preferably selected accordingly to fit channelcoding blocks. The buffered data contains 48 pilot chip samples at thefront, 48 pilot chip samples in the end, and 2 MAC portions 106, 112enclosing 2 traffic data portions 108, 110.

Although embodiments of the invention are described below primarily inthe context of a buffered data block as shown in FIG. 4, it should beappreciated that other buffering schemes may be used, to equalize thecontrol or traffic blocks 100, 108, for example, in a substantiallysimilar manner using the pilot chips 104 and the MAC chips 102, 106.

For simplicity, the buffered complex data samples are denoted r(0),r(1),. . . ,r(1023). Of course, other numbers of samples may be used,although powers of 2 may be preferred. Estimated time domain channelimpulse response are similarly denoted ch(0),ch(1), . . . ,ch(N), whereN is selected to cover the targeted the delay spread of the environmentand the non-Nyquist ICI effects, and is 14 in one embodiment.

The pilot portions, which contain a known data sequence or pattern, mayfirst be extracted from both ends of the buffered data. This might beaccomplished, for example, using a short scrambling code determinedaccording to the index of a starting point of the data block. Assumingthat corresponding pilot scrambling code segments are respectivelyspn(0), spn(1), . . . ,spn(47) and spn(975),spn(976), . . . ,spn(1023),a prefix z(n) may be generated as follows:For n=0:N−1${z(n)} = {{\sum\limits_{k = 0}^{n}{{{spn}(k)}{{ch}\left( {n - k} \right)}}} + {\sum\limits_{k = {1024 - N + n}}^{1023}{{{spn}(k)}{{ch}\left( {1024 + n - k} \right)}}}}$end

Replacing the first N received samples by z(0), . . . ,z(N−1), the newbuffered data is z(0),z(1), . . . ,z(N−1),r(N), . . . ,r(1023) Thisrepresents one mechanism for translating a received CDMA signal, whichis a linear convolution between a transmitted CDMA signal and amultipath communication channel, into a new CDMA signal which is acyclic convolution with a channel estimate.

More generally, in some embodiments, the effects of interference from apreceding transmission, typically MAC or pilot, are removed from thebuffered data by reconstructing the interference and subtracting it.Such known or repeated data sequences in a known portion of a signal mayalso be removed from a received signal in other embodiments.

The re-constructed channel taps ch(0),ch(1), . . . ,ch(N) are preferablyconverted from the time domain to the frequency domain. In oneembodiment, a DFT (Discrete Fourier Transform) of the same size as thebuffered data block size, 1024 in this example, is used for time tofrequency domain conversion, although other types of transform orconversion are also contemplated. Frequency domain components of thechannel taps are denoted cf(0),cf(1), . . . ,cf(N−1),cf(N), . . .,cf(1023) for the following description.

The received and buffered data block is also preferably converted intothe frequency domain, using a DFT or another transform or conversion toyield rf(0),rf(1), . . . ,rf(N−1),rf(N), . . . ,rf(1023). In someembodiments, the received data block or portions thereof may includefrequency domain components which may be used directly in frequencydomain equalization. For example, the symbol demultiplexer 22 in thetransmit chain of FIG. 1 converts frequency domain symbols into the timedomain. However, if frequency domain components are transmitted to areceiver, then at least a portion of the time to frequency domainconversion may be avoided at the receiver, to thereby effectively splitequalization processing between a transmitter and a receiver. In thissense, a transmitter may assist with processing operations to beperformed at a receiver.

Multipath effects may then be reduced in the frequency domain byperforming a component-wise complex division, or a maximum likelihooddetection, etc. Here we use a simple complex division, for example toproduce a frequency domain representation of an equalized signalre(k)=rf(k)/cf(k).

The resultant equalized data block may then be converted back into atime domain signal by performing an IDFT (Inverse DFT) or otherconversion on the data block re(0),re(1), . . . ,re(1023). The convertedtime domain output includes an equalized data stream, which may befurther processed, to be de-scrambled and then decoded for instance.

Thus, more generally, a method according to an embodiment of theinvention may include the operations shown in the flow diagram of FIG.5. The method of FIG. 5 relates to equalizing a portion of a CDMA signalreceived over a multipath communication channel. The CDMA signal has adata portion and a known portion which includes a known data sequence.

The method 120 includes determining at 122, from the known portion, achannel estimate of the communication channel. At 124, a frequencydomain representation of the CDMA signal is adjusted using the channelestimate to produce a frequency domain equalized signal. Adjusting at124 may include performing a component-wise division of the frequencydomain representation of the CDMA signal by the frequency domain channelestimate, for example, to produce the frequency domain equalized signal.

The channel estimate may initially be determined at 122 as a time domainchannel estimate and then converted to a frequency domain channelestimate, using a DFT, for example, for use in adjusting the frequencydomain signal at 124.

The method also preferably includes an operation co translate a receivedCDMA signal, which represents a linear convolution between a transmittedsignal and a multipath channel, into a new CDMA signal which is a cyclicconvolution with the channel estimate. Replacement or removal of theknown portion of a received signal or its interference effects, asdescribed above, are examples of techniques which may be used toaccomplish such a translation. This translation function may alsoinvolve time/frequency domain conversions, depending upon the domain inwhich the translation is to be performed. The resultant new CDMA signalis then preferably adjusted at 124.

In one embodiment, a method also includes operations of reconstructingan interference effect of the known portion upon the data portion usingthe time domain channel estimate and subtracting the interference effectfrom the data portion to produce an interference compensated portion ofthe CDMA signal. The interference compensated portion of the CDMA signalis then converted to the frequency domain to produce the frequencydomain representation of the CDMA signal.

According to another embodiment of the invention, the method includesreplacing at least some of the known portion of the CDMA signal with anew portion to convert the CDMA signal to the new CMDA signal which is acyclic convolution with the time domain channel estimate. The frequencydomain representation of the CDMA signal is produced by performing atime domain to frequency domain conversion on the new CDMA signal.

Effects of the communication channel as represented by the frequencydomain channel estimate are removed from the frequency domainrepresentation of the CDMA signal in a further embodiment of theinvention.

ISI effects may also or instead be removed from the CDMA signal usingthe time domain channel estimate to produce an interference compensatedCDMA signal, which may be converted to the frequency domain to producethe frequency domain representation of the CDMA signal.

Considering channel estimation in further detail in the context or theabove example slot structure, there are two blocks of pilot data duringeach slot that can be used to estimate the time domain channel impulseresponse. For the purposes of illustration, it is assumed thattransmitted chip data {s(k)} will go through a multi-path channeldefined by${{{ch}(t)} = {\sum\limits_{l - 1}^{N_{\tau}}{{\alpha(l)}{h\left( {t - {\tau(l)}} \right)}}}},$with random delays and Rayleigh fading on each path. The channel impulseresponse ch(t) will be relatively stable within a full slot or half aslot. In this multi-path channel, there are N_(r) significant paths. τ(l) is the delay of l^(th) path and α(l) is the corresponding channel gainwhich belongs to a Rayleigh distribution. Note that all the delays willrefer to the same clock, (e.g. the frame/slot boundary captured aftersystem acquisition).

On a receiving terminal side, the received baseband signal can bemodeled as:${{r(t)} = {{\sum\limits_{n}{{s(n)}{{ch}\left( {t - {nT}} \right)}}} + {n(t)}}},$with n(r) representing noise.

Suppose the sampling rate is Mf_(c), which represents M samples perchip. A synchronization module or finger detection module at thereceiving terminal will find the strongest path, illustratively pathnumber two although any path might be strongest, with a timing/fingerreference of τ′(2), which can be directly related to an Mf_(c), index.Note that Δ=τ′(2)−τ(2) might not be zero due to the sampling resolution,but a smaller Δ may be generally preferred. Decimation to 1f_(c)sampling yields $\begin{matrix}{{r(k)} = {r\left( {{kT} + {\tau^{\prime}(2)}} \right)}} \\{= {{\sum\limits_{n}{{s(n)}{{ch}\left( {{kT} + {\tau^{\prime}(2)} - {nT}} \right)}}} + {n({kT})}}} \\{= {{{\alpha(2)}{\sum\limits_{n}{{s(n)}{h\left( {{kT} + \Delta - {nT}} \right)}}}} +}} \\{\sum\limits_{n}{{s(n)}{\overset{N_{r}}{\sum\limits_{l \neq 2}}{{\alpha(l)}{h\left( {{kT} + {\tau^{\prime}(2)} - {\tau(l)} - {nT}} \right)}}}}} \\{= {{{\alpha(2)}{\sum\limits_{n}{{s(n)}{h\left( {{\left( {k - n} \right)T} + \Delta} \right)}}}} +}} \\{\sum\limits_{n}{{s(n)}{\sum\limits_{l \neq 2}^{N_{r}}{{\alpha(l)}{{h\left( {{\left( {k - n} \right)T} + {\tau(2)} - {\tau(l)} + \Delta} \right)}.}}}}}\end{matrix}$

Note that the clock now is only locking to the open-eye point τ′(2). Ifthis open eye is exact, then Δ will disappear. Otherwise, Δ will affectall other paths. In implementation, reference can still be made to theframe/slot boundaries by converting the relative timings.

For the purpose of channel reconstruction, the observed data {r(k)} maybe used to reconstruct the overall channel as $\begin{matrix}{{{ch}(m)} = {{ch}\left( {{mT} + {\tau^{\prime}(2)}} \right)}} \\{= {{{\alpha(2)}{h\left( {{mT} + \Delta} \right)}} + {\sum\limits_{l \neq 2}^{N_{r}}{{\alpha(l)}{{h\left( {{mT} + {\tau^{\prime}(2)} - {\tau(l)}} \right)}.}}}}}\end{matrix}$

Assuming that the number of channel taps is N+1 and ch(m)=0 when m<0 andm>N, then the above equation can be simply re-expressed as$\begin{matrix}{{r(k)} = {{\sum\limits_{n}{{s(n)}{{ch}\left( {k - n} \right)}}} + {n({kT})}}} \\{= {{\sum\limits_{n = {k - N}}^{n = k}{{s(n)}{{ch}\left( {k - n} \right)}}} + {{n({kT})}.}}}\end{matrix}$

This equation is the basis for the LMS (Least Mean Square) channelestimation. As described above, {r(k)} is the received data sequence andknown sequences are periodically transmitted and therefore received inthe receiving terminal.

Now we suppose that a portion of known chip sequences are transmittedstarting from index K₁ and end at the last known chip K₂. From thepreceding equation, it can be seen that the received data sequencer(K₁+N), . . . ,r(K₂) is the only portion which is fully attributable tothe known sequence s(K₁), . . . s(K₂). The transmitter timing cantherefore also be derived from received data timing, resulting in thefollowing shortened linear equations based on the preceding equationwith this portion of the known sequence: $\begin{matrix}{{r(k)} = {{\sum\limits_{n}{{s(n)}{{ch}\left( {k - n} \right)}}} + {n({kT})}}} & \\{{\sum\limits_{n = {k - N}}^{n = k}{{s(n)}{{ch}\left( {k - n} \right)}}} + {n({kT})}} & {{k = {K_{1} + N}},\ldots\quad,{K_{2}.}}\end{matrix}$

In matrix form, $\begin{bmatrix}{s\left( K_{1} \right)} & {s\left( {K_{1} + 1} \right)} & \ldots & {s\left( {K_{1} + N} \right)} \\{s\left( {K_{1} + 1} \right)} & {s\left( {K_{1} + 2} \right)} & \ldots & {s\left( {K_{1} + N + 1} \right)} \\\ldots & \ldots & \ldots & \ldots \\{s\left( {K_{2} - N} \right)} & {s\left( {K_{2} - N + 1} \right)} & \ldots & {s\left( K_{2} \right)}\end{bmatrix}{\quad{{\begin{bmatrix}{{ch}(N)} \\{{ch}\left( {N - 1} \right)} \\\vdots \\{{ch}(0)}\end{bmatrix} + \quad\begin{bmatrix}{n\left( K_{1} \right)} \\{n\left( {K_{1} + 1} \right)} \\\vdots \\{n\left( {K_{2} - N} \right)}\end{bmatrix}} = {\begin{bmatrix}{r\left( {K_{1} + N} \right)} \\{r\left( {K_{1} + N + 1} \right)} \\\vdots \\{r\left( K_{2} \right)}\end{bmatrix}.}}}$

Such a set of a linear equations has N+1 unknowns and K2−K1−N equations.Particularly, with the 96 continuous known pilot chips, in two pilotblocks in the above example, we have 96−N equations, as illustrated inFIG. 6. The curve in FIG. 6 illustrates receiver timing versustransmitter timing, and the capture of an entire multipath impulseresponse using relative timing. Two portions of known data may bestaggered, which can result in double equations and so on, or channelestimation may be performed substantially separately based on each knownportion, with an average of the estimated channels being used as a finalchannel estimate.

In any case, generic linear equations such as those above are to beresolved during channel estimation. Because of noise, these equationsare preferably resolved by LMS methods. An explicit solution may beexpressed as ${\begin{bmatrix}{{ch}(N)} \\{{ch}\left( {N - 1} \right)} \\\vdots \\{{ch}(0)}\end{bmatrix} = {\left( {S^{T}S} \right)^{- 1}{S^{T}\begin{bmatrix}{r\left( {K_{1} + N} \right)} \\{r\left( {K_{1} + N + 1} \right)} \\\vdots \\{r\left( K_{2} \right)}\end{bmatrix}}}},{where}$ $S = {\begin{bmatrix}{s\left( K_{1} \right)} & {s\left( {K_{1} + 1} \right)} & \ldots & {s\left( {K_{1} + N} \right)} \\{s\left( {K_{1} + 1} \right)} & {s\left( {K_{1} + 2} \right)} & \ldots & {s\left( {K_{1} + N + 1} \right)} \\\ldots & \ldots & \ldots & \ldots \\{s\left( {K_{2} - N} \right)} & {s\left( {K_{2} - N + 1} \right)} & \ldots & {s\left( K_{2} \right)}\end{bmatrix}.}$

A more efficient way to derive the solution is to solve the followinglinear equations directly: ${S^{T}{S\begin{bmatrix}{{ch}(N)} \\{{ch}\left( {N - 1} \right)} \\\vdots \\{{ch}(0)}\end{bmatrix}}} = {{S^{T}\begin{bmatrix}{y\left( {K_{1} + N} \right)} \\{y\left( {K_{1} + N + 1} \right)} \\\vdots \\{y\left( K_{2} \right)}\end{bmatrix}}.}$

It is worthy to note that the coefficient matrix of this linear equationis an integer Hermitian matrix of dimension (N+1)×(N+1). Either Choleskyor SVD (Singular Value Decomposition) methods can be used to solve theselinear equations. The particular decomposition method to be used is adesign option. On the other hand, the matrix S is only related to thescrambling code in some embodiments and therefore can be formulated justafter a communication link is set up. The decomposition is alsopreferably performed only once per link and used until the link isterminated.

A time domain channel estimate may be used to perform time domainequalization, although the complexity of time domain equalization isexpected to be approximately 8 times that of frequency domainequalization.

In an embodiment of the invention described above, equalization involvescomplex division, in which small values of cf(k) may enhance noise.Although the above division simplifies the implementation, it might notbe optimal in a noisy and fading environment. For example, the multipathchannel may have either a null or a notch in the frequency domain.Unlike OFDM, this noise enhancement affects a subsequent IFFT result andit may therefore represent a global effect. In order to mitigate thisdrawback, further techniques as described below may be used, albeit withmore implementation complexity.

Suppose β is a predefined threshold which reflects the system tolerancefor noise enhancement. Frequency tones can then be classified into twosets, i.e. a “good” or favorable set Ω and a “bad” or unfavorable set ψ,which are defined asΩ={k∥cf(k)|>β}, ψ={k∥cf(k)|≦β}.

It will be apparent that good tones kεΩ will not enhance the noise orwill enhance by a tolerable amount such that an equalizer may use thecomplex division scheme described above, whereas bad tones kεψ willenhance the noise too much and therefore the division is not feasible.

In one embodiment, each rf(k) for kεψ is multiplied by β. According toanother embodiment, weights are determined and applied to the componentsrf (k) for kεψ.

An example weight calculation technique defines${{d(m)} = {{{spn}(m)} - {\sum\limits_{k \in \Omega}^{\quad}{\frac{{rf}(k)}{{cf}(k)}{\exp\left( {{jmk}\frac{2\pi}{1024}} \right)}}}}},{m = 0},1,\ldots\quad,47.$

It is noted that spn(0),spn(1), . . . ,spn(47) are the known pilot chipsin front of a buffered data block. Solutions to the following quadraticoptimization provide optimal weights ω.$\min{\sum\limits_{m = 0}^{47}{{{{\sum\limits_{k \in \Psi}^{\quad}{{\omega(k)}{{rf}(k)}{\exp\left( {{jmk}\frac{2\pi}{1024}} \right)}}} - {d(m)}}}^{2}.}}$

If the number of bad tones is less than some number, for example 48 (thelast 48 known chips can be used to handle up to 96 bad tones), the aboveoptimization has a unique solution with explicit formulaω=(E _(ψ) ^(*) E _(ψ))⁻¹ E _(ψ) ^(*) d,where E_(ψ) is a matrix formed by both rf(k) and$\exp\left( {{jmk}\frac{2\pi}{1024}} \right)$for kεψ and m=0,1, . . . ,47. Note that the matrix E_(ψ) has a veryspecial structure and therefore can be inverted very efficiently. Afterthis optimization calculation, the equalized frequency domain data blockbecomes re(k)=rf(k)|cf(k), kεΩ and re(k)=ω(k)rf (k), kεψ.

The preceding weight calculation equations assume a buffered blocklength of 1024 chips and 48 pilot chips. However, it should beappreciated that the invention is in no way limited to these particularlengths. In general, weights may be calculated in a substantiallysimilar manner for any known data pattern length a and block length b .

FIG. 7 is a block diagram of a system in which embodiments of theinvention may be implemented. The system includes communicationequipment 130, 132 connected by a communication link 131. It will beapparent to those skilled in the art, however, that a communicationsystem may include many more than two installations of communicationequipment between which communications may be established.

Although shown in FIG. 7 as a connection, the link 131 need notnecessarily be a physical connection. For example, in one embodiment,the communication equipment 130 and 132 are a network element and acommunication terminal, respectively, in a wireless communicationsystem. The link 131 also need not be a direct connection, and mayinclude connections through one or more networks or interveningcomponents, for example.

Communication equipment 130 includes a processor 136 connected to amemory 134, and a transceiver 140. Communication equipment 132 has asimilar structure, including a processor 144 connected to memory 146,and a transceiver 142. It should be appreciated that other componentsthan those explicitly shown in FIG. 7 may be provided, depending uponthe particular type of the communication equipment 130, 132. It shouldalso be noted that although the communication equipment 130, 132 havethe same general structure in FIG. 7, embodiments of the invention maybe implemented in conjunction with substantially different communicationequipment. In the above example of a network element and a communicationterminal, both the network element and the communication terminal mayinclude a processor, a memory, and a transceiver, as shown, but areotherwise very different equipment.

The processor 136 may be a microprocessor which executes software storedin the memory 134. The processor 136 may instead be implemented as amicrocontroller, a DSP (digital signal processor), an ASIC (ApplicationSpecific Integrated Circuit), or other processing element. Embodimentsof the invention may be implemented using a dedicated processor or aprocessor which also performs other functions. For example, theprocessor 136 may execute operating system software and softwareapplications to support functions other than those disclosed herein.

The memory 134 represents a memory device, and may include, for example,any of solid state memory devices, disk drives, and other memory devicesadapted to operate with fixed or removable memory media.

The transceiver 140 enables communication with the communicationequipment 132 via the communication link 131. Many different types oftransceiver 140 will be apparent to those skilled in the art, for use inconjunction with corresponding types of communication link. Embodimentsin which the transceiver 140 includes components to enablecommunications over multiple types of communication link are alsocontemplated. It should be appreciated that the invention is in no waylimited to implementation in conjunction with communication equipmentwhich is capable of two-way communications. Thus, the equalizationtechniques disclosed herein may be implemented at communicationequipment which includes a receiver instead of the transceiver 140.Similarly, transmit-side functions may be performed at communicationequipment which includes only a transmitter.

The processor 144, transceiver 142, and memory 146 in communicationequipment 132 may be substantially similar to the processor 136, memory134, and transceiver 140 in communication equipment 130, describedabove.

In operation, transmitting communication equipment, illustrativelycommunication equipment 130, generates a CDMA signal for transmission toreceiving communication equipment, illustratively communicationequipment 132. As the communication equipment 130, 132 includetransceivers 140, 142 which may send or receive signals, these exampledesignations of transmitter and receiver are intended solely forillustrative purposes. In the system of FIG. 7, communication signalsmay be sent in either direction on the link 131.

According to the above example in which communication equipment 130 isto transmit a signal to communication equipment 132, the processor 136is configured, by executing software in the memory 134 for instance, toreceive from an input data to be transmitted, and to multiplex the dataand a known or repeated data sequence into a CDMA signal. The CDMAsignal is then output for transmission. Transmission of the signal maybe substantially in real time when the signal is output or at a latertime, in which case the signal may be stored in the memory 134, forexample. The multiplexed data may include time domain components and/orfrequency domain components. As described above, where frequency domaincomponents are multiplexed into the CDMA signal, the amount ofprocessing associated with performing time domain to frequency domainconversion at a receiver prior to frequency domain equalization isreduced. In one embodiment, the processor 136 implements a conversionengine, illustratively an IDFT or IFFT engine, for converting frequencydomain components generated during encoding of the data into time domaincomponents.

At receiving communication equipment 132, the processor 144 isconfigured to receive the CDMA signal from an input, which may beconnected to the transceiver 142, to determine from the known datasequence a frequency domain channel estimate, and to adjust a frequencydomain representation of the CDMA signal using the frequency domainchannel estimate to produce a frequency domain representation of anequalized signal. Configuration of the processor 144, as for theprocessor 136 described above, may be accomplished by providing softwarein the memory 146 for execution by the processor 144, for example.

The processor 144 may convert received time domain components of theCDMA signal or a determined time domain channel estimate intocorresponding frequency domain components. This conversion function maybe supported, for example, by a conversion engine such as a DFT or anFFT engine implemented in software in the memory 146. Conversion of anequalized frequency domain signal to the time domain may similarly beprovided by an IDFT or IFFT engine, for example.

The memory 146 may also be used to store the CDMA signal or portionsthereof. With reference to FIG. 4, 1024 chips of a received CDMA signalare stored in the memory 146 in one embodiment of the invention.

Other functions may also be performed by the processors 136 and 144,including additional equalization functions as described above and/orfurther signal processing functions, such as de-scrambling and normalCDMA signal decoding to recover and output transmitted data. Separateprocessors or functional elements may instead be provided forequalization, de-scrambling, decoding, and other operations. Therefore,although only a single processor has been shown in communicationequipment 130, 132 in FIG. 7, embodiments of the invention may beimplemented with one or more elements embodying equalization,de-scrambling, decoding, and other receiving operations, andcorresponding operations at transmitting communication equipment.

In a preferred embodiment of the invention, frequency domainequalization is implemented for forward links in a wirelesscommunication network, such that transmitting operations are supportedat network elements such as base stations and receiving operations aresupported at communication terminals. However, frequency domainequalization may also or instead be implemented on reverse links.

Embodiments of the invention can be added to existing communicationequipment, for example, by including extra transform functionality, suchas DFT/IDFT or FFT/IFFT for conversion from the time domain to thefrequency domain for equalization and conversion of an equalized signalfrom the frequency domain to the time domain. This might be integratedonto an existing chip, or provided in a separate chip. It can beimplemented in hardware, software, or some combination thereof.

What has been described is merely illustrative of the application of theprinciples of the invention. Other arrangements and methods can beimplemented by those skilled in the art without departing from the scopeof the present invention.

For example, although described primarily in the context of methods andsystems, other implementations of the invention are also contemplated,such as in instructions stored on a computer-readable medium.

1. A method of equalizing a CDMA signal received over a multipathcommunication channel, the CDMA signal having a data portion and a knownportion comprising a known or repeated data sequence and representing alinear convolution between the multipath channel and a transmitted CDMAsignal, the method comprising: determining from the known portion achannel estimate of the communication channel; translating the CDMAsignal into a new CDMA signal which comprises a cyclic convolution withthe channel estimate; and adjusting a frequency domain representation ofthe new CDMA signal using the channel estimate to produce a frequencydomain representation of an equalized signal.
 2. The method of claim 1,wherein determining comprises determining a time domain channel estimatefrom the known portion, and wherein adjusting comprises performing atime domain to frequency domain conversion on the time domain channelestimate to produce a frequency domain channel estimate and adjustingthe frequency domain representation of the new CDMA signal using thefrequency domain channel estimate.
 3. The method of claim 2, whereintranslating comprises subtracting the known portion from the CDMA signalto produce the new CDMA signal.
 4. The method of claim 2, whereintranslating comprises replacing at least some of the known portion witha new portion which converts the CDMA signal to the new CMDA signalwhich is a cyclic convolution with the time domain channel estimate. 5.The method of claim 2, wherein adjusting comprises: removing the effectof the channel as represented by the frequency domain channel estimatefrom the frequency domain representation of the new CDMA signal.
 6. Themethod of claim 2, wherein translating comprises removing ISI(inter-symbol interference) effects from the CDMA signal using the timedomain channel estimate to produce the new CDMA signal.
 7. The method ofclaim 1, further comprising; performing a frequency domain to timedomain conversion on the frequency domain representation of an equalizedsignal to produce a time domain equalized signal.
 8. The method of claim1, wherein the known portion comprises at least one of a preceding knownportion preceding the data portion and a succeeding known portionfollowing the data portion.
 9. The method of claim 1, wherein the knownportion comprises at least one of pilot channel signalling and MAC(Media Access Control) channel signalling.
 10. The method of claim 1,wherein the CDMA signal comprises 1024 chips, including two data blocksof 400 chips each as the data portion, preceding and succeeding MACblocks of 64 chips each which precede and follow the data portion,respectively, and preceding and succeeding pilot blocks of 48 chips eachwhich precede and follow the data portion, respectively, as the knownportion.
 11. The method of claim 4, further comprising; generating thenew portion of the CDMA signal as${{{z(n)} = {{{\sum\limits_{k = 0}^{n}{{{spn}(k)}{{ch}\left( {n - k} \right)}}} + {\sum\limits_{k = {1024 - N - n}}^{1023}{{{spn}(k)}{{ch}\left( {1024 + n - k} \right)}\quad{for}\quad n}}} = 0}};{N - 1}},$where N is selected to cover a targeted delay spread and theinterference effects; spn(k)={spn(0),spn(1), . . . ,spn(47)} and{spn(975),spn(976), . . . ,spn(1023)} comprises pilot scrambling codesegments for pilot signalling comprising the known portion; andch(k)=ch(0),ch((1), . . . ,ch(N) comprises the time domain channelestimate.
 12. The method of claim 7, further comprising: performingfurther processing on the time domain equalized signal, the furtherprocessing comprising at least one of de-scrambling and normal CDMAdecoding.
 13. The method of claim 2, wherein determining the time domainchannel estimate comprises solving: ${{{\begin{bmatrix}{s\left( K_{1} \right)} & {s\left( {K_{1} + 1} \right)} & \cdots & {s\left( {K_{1} + N} \right)} \\{s\left( {K_{1} + 1} \right)} & {s\left( {K_{1} + 2} \right)} & \cdots & {s\left( {K_{1} + N + 1} \right)} \\\cdots & \cdots & \cdots & \cdots \\{s\left( {K_{1} - N} \right)} & {s\left( {K_{1} - N + 1} \right)} & \cdots & {s\left( K_{2} \right)}\end{bmatrix}\left\lbrack \quad\begin{matrix}{{ch}(N)} \\{{ch}\left( {N - 1} \right)} \\\vdots \\{{ch}(0)}\end{matrix} \right\rbrack} + \left\lbrack \begin{matrix}{n\left( K_{1} \right)} \\{n\left( {K_{1} + 1} \right)} \\\vdots \\{n\left( {K_{2} - N} \right)}\end{matrix}\quad \right\rbrack} = \begin{bmatrix}{y\left( {K_{1} + N} \right)} \\{y\left( {K_{1} + N + 1} \right)} \\\vdots \\{y\left( K_{2} \right)}\end{bmatrix}},$ where s(i) comprises an i^(th) component of the knownportion; ch(i) comprises an i^(th) component of the time domain channelestimate; n(i) comprises an i^(th) component of noise; r(i) comprises ani^(th) component of the CDMA signal; K₁ is a starting index of the knownportion; K₂ is an end index of the known portion; and N is a number ofcomponents in the frequency domain channel estimate.
 14. The method ofclaim 2, wherein adjusting comprises performing a component-wisedivision of the frequency domain representation of the new CDMA signalby the frequency domain channel estimate.
 15. The method of claim 14,wherein the component-wise division is performed only for values of thefrequency domain channel estimate which are sufficiently large so asreduce effects of amplifying noise components of the CDMA signal. 16.The method of claim 14, wherein the component-wise division is performedonly for components of the frequency domain channel estimate which havevalues above a predefined threshold value β.
 17. The method of claim 16,further comprising: multiplying by β each component of the frequencydomain representation of the new CDMA signal for which the correspondingcomponent of the frequency domain channel estimate has a value below β.18. The method of claim 16, further comprising: determining weights forcomponents of the frequency domain channel estimate which have valuesless than β; multiplying by a respective determined weight eachcomponent of the frequency domain representation of the new CDMA forwhich the corresponding component of the frequency domain channelestimate has a value below β.
 19. The method of claim 18, whereindetermining weights comprises determining the weights ω asω=(E ^(*) _(ψ) E _(ψ))⁻¹ E ^(*) _(ψ) d, where${d = {\left\{ {d(m)} \right\} = {{{spn}(m)} - {\sum\limits_{k \in \Omega}^{\quad}{\frac{{rf}(k)}{{cf}(k)}{\exp\left( {{jmk}\frac{2\pi}{b}} \right)}}}}}};$m=0,1, . . . ,a_(i) a is a length of the known portion; b is a length ofa portion of the CDMA signal to be equalized; spn(m) comprises an m^(th)component of the known portion; rf(k) comprises a k^(th) component ofthe frequency domain representation of the new CDMA signal; cf(k)comprises a k^(th) component of the frequency domain channel estimate;E_(ψ) comprises a matrix formed by both rf(k) and$\exp\left( {{jmk}\frac{2\pi}{b}} \right)$ for kεψ and m=0,1, . . . ,a,and ψ comprises indices of the components of the frequency domainchannel estimate having values less than β.
 20. The method of claim 1,wherein the data portion of the CDMA signal comprises frequency domaincomponents.
 21. A computer program product comprising instructions whichwhen executed perform the method of claim
 1. 22. The method of claim 1,implemented at a receiver, further comprising: multiplexing the dataportion and the known portion into the CDMA signal at a transmitter; andtransmitting the CDMA signal from the transmitter to the receiver. 23.The method of claim 22, wherein multiplexing comprises; assisting intranslating from the linear convolution to the cyclic convolution at thereceiver end by: generating frequency domain components from informationto be transmitted; performing a frequency domain to time domainconversion on the frequency domain components to produce time domaincomponents; and multiplexing the time domain components into the CDMAsignal to form the data portion.
 24. The method of claim 23, whereinmultiplexing comprises; generating frequency domain components frominformation to be transmitted; and multiplexing the frequency domaincomponents into the CDMA signal to form the data portion.
 25. Acommunication signal processing method comprising: multiplexing a dataportion and a known portion comprising a known or repeated data sequenceinto a CDMA signal; and outputting the CDMA signal for transmission to areceiver over a multipath communication channel and equalization at thereceiver by determining from the known portion a channel estimate of thecommunication channel, translating the CDMA signal into a new CDMAsignal which comprises a cyclic convolution with the channel estimate,and adjusting a frequency domain representation of the new CDMA signalusing the channel estimate to produce a frequency domain representationof an equalized signal.
 26. The method of claim 25, wherein multiplexingcomprises: multiplexing frequency domain components representing thedata into the CDMA signal.
 27. A system for equalizing a portion of aCDMA signal received over a multipath communication channel, the CDMAsignal having a data portion and a known portion comprising a known orrepeated data sequence and representing a linear convolution between themultipath channel and a transmitted CDMA signal, the system comprising:an input; and a processor configured to receive the CDMA signal from theinput, to determine from the known portion a channel estimate of thecommunication channel, to translate the CDMA signal into a new CDMAsignal which comprises a cyclic convolution with the channel estimate,and to adjust a frequency domain representation of the new CDMA signalusing the channel estimate to produce a frequency domain representationof an equalized signal.
 28. The system of claim 27, wherein theprocessor is configured to determine the channel estimate by determininga time domain channel estimate from the known portion, to perform a timedomain to frequency domain conversion on the time domain channelestimate to produce a frequency domain channel estimate, and to adjustthe frequency domain representation of the new CDMA signal using thefrequency domain channel estimate.
 29. The system of claim 28, whereinthe processor implements a transform engine for performing the timedomain to frequency domain conversion.
 30. The system of claim 28,wherein the processor is further configured to translate the CDMA signalby subtracting the known portion from the CDMA signal to produce the newCDMA signal.
 31. The system of claim 28, wherein the processor isfurther configured to translate the CDMA signal by replacing at leastsome of the known portion with a new portion which converts the CDMAsignal to the new CMDA signal which is a cyclic convolution with thetime domain channel estimate.
 32. The system of claim 28, wherein theprocessor is configured to adjust the frequency domain representation ofthe new CDMA signal by removing the effect of the channel as representedby the frequency domain channel estimate from the frequency domainrepresentation of the new CDMA signal.
 33. The system of claim 28,wherein the processor is further configured to translate the CDMA signalby removing ISI (inter-symbol interference) effects from the CDMA signalusing the time domain channel estimate to produce the new CDMA signal.34. The system of claim 27, wherein the processor is further configuredto perform a frequency domain to time domain conversion on the frequencydomain representation of an equalized signal to produce a time domainequalized signal.
 35. The system of claim 27, wherein the known portioncomprises at least one of a preceding known portion preceding the dataportion and a succeeding known portion following the data portion. 36.The system of claim 27, wherein the CDMA signal comprises an 1xEV-DOsignal.
 37. The system of claim 27, further comprising: a memory,wherein the processor is further configured to store a portion of theCDMA signal in the memory.
 38. The system of claim 31, wherein theprocessor is further configured to generate the new portion of the CDMAsignal as${{z(n)} = {{{\sum\limits_{k = 0}^{n}{{{spn}(k)}{{ch}\left( {n - k} \right)}}} + {\sum\limits_{k = {1024 - N + n}}^{1023}{{{spn}(k)}{{ch}\left( {1024 + n - k} \right)}\quad{for}\quad n}}} = {0:{N - 1}}}},$where N is selected to cover a targeted delay spread and theinterference effects; spn(k)={spn(0), spn(1), . . . ,spn(47)} and{spn(975),spn(976), . . . , spn(1023)} comprises pilot scrambling codesegments for pilot signalling comprising the known portion; andch(k)=ch(0),ch(1), . . . ,ch(N) comprises the time domain channelestimate.
 39. The system of claim 28, wherein the processor isconfigured to determine the time domain channel estimate by solving:${{{\begin{bmatrix}{s\left( K_{1} \right)} & {s\left( {K_{1} + 1} \right)} & \cdots & {s\left( {K_{1} + N} \right)} \\{s\left( {K_{1} + 1} \right)} & {s\left( {K_{1} + 2} \right)} & \cdots & {s\left( {K_{1} + N + 1} \right)} \\\cdots & \cdots & \cdots & \cdots \\{s\left( {K_{2} - N} \right)} & {s\left( {K_{2} - N + 1} \right)} & \cdots & {s\left( K_{2} \right)}\end{bmatrix}\left\lbrack \quad\begin{matrix}{{ch}(N)} \\{{ch}\left( {N - 1} \right)} \\\vdots \\{{ch}(0)}\end{matrix} \right\rbrack} + \left\lbrack \begin{matrix}{n\left( K_{1} \right)} \\{n\left( {K_{1} + 1} \right)} \\\vdots \\{n\left( {K_{2} - N} \right)}\end{matrix}\quad \right\rbrack} = \begin{bmatrix}{y\left( {K_{1} + N} \right)} \\{y\left( {K_{1} + N + 1} \right)} \\\vdots \\{y\left( K_{2} \right)}\end{bmatrix}},$ where s(i) comprises an i^(th) component of the knownportion; ch(i) comprises an i^(th) component of the time domain channelestimate; n(i) comprises an i^(th) component of noise; r(i) comprises ani^(th) component of the CDMA signal; K₁ is a starting index of the knownportion; K₂ is an end index of the known portion; and N is a number ofcomponents in the frequency domain channel estimate.
 40. The system ofclaim 31, wherein the processor is further configured to adjust thefrequency domain representation of the new CDMA signal by performing acomponent-wise division of the frequency domain representation of thenew CDMA signal by the frequency domain channel estimate.
 41. The systemof claim 40, wherein the processor is further configured to perform thecomponent-wise division only for components of the frequency domainchannel estimate which have values above a predefined threshold value.42. The system of claim 41, wherein the processor is further configuredto multiply by the predefined threshold value each component of thefrequency domain representation of the new CDMA signal for which thecorresponding frequency domain channel estimate has a value below thepredefined threshold value.
 43. The system of claim 41, wherein theprocessor is further configured to multiply by a respective weight eachfrequency domain representation of the new CDMA signal for which thecorresponding component of the frequency domain channel estimate whichhas a value below the predefined threshold value.
 44. The system ofclaim 27, implemented at a receiver in a communication system, thecommunication system further comprising: a transmitter comprising aninput and a processor configured to receive from the input data fortransmission to the receiver, to multiplex the data and the known orrepeated data sequence to form the data portion and the known portion ofthe CDMA signal, and to output the CDMA signal for transmission from thetransmitter to the receiver.
 45. The system of claim 44, wherein theprocessor is further configured to assisting in translating from thelinear convolution to the cyclic convolution at the receiver end bygenerating frequency domain components from the data, and to multiplexthe frequency domain components to form the data portion of the CDMAsignal.
 46. A communication signal processing system comprising: aninput for receiving data to be transmitted; and a processor configuredto receive the data from the input, to multiplex the data and a known orrepeated data sequence into a CDMA signal to form a data portion and aknown portion, and to output the CDMA signal for transmission to areceiver over a multipath communication channel and equalization at thereceiver by determining from the known portion a channel estimate of thecommunication channel, translating the CDMA signal into a new CDMAsignal which comprises a cyclic convolution with the channel estimate,and adjusting a frequency domain representation of the new CDMA signalusing the channel estimate to produce a frequency domain representationof an equalized signal.
 47. The system of claim 46, wherein theprocessor is configured to multiplex the data into the CDMA signal bymultiplexing frequency domain components representing the data into theCDMA signal.
 48. A CDMA communication system comprising: communicationequipment comprising a processor configured to receive from an inputdata to be transmitted, to multiplex the data and a known or repeateddata sequence into a CDMA signal to form a data portion and a knownportion, and to output the CDMA signal for transmission; andcommunication equipment comprising a processor configured to receive theCDMA signal over a multipath communication channel, to determine fromthe known portion a channel estimate of the communication channel, totranslate the CDMA signal into a new CDMA signal which comprises acyclic convolution with the channel estimate, and to adjust a frequencydomain representation of the new CDMA signal using the channel estimateto produce a frequency domain representation of an equalized signal. 49.The communication system of claim 48, wherein at least one networkelement of the communication system comprises the communicationequipment comprising a processor configured to receive from an inputdata to be transmitted.
 50. The communication system of claim 48,wherein at least one network element of the communication systemcomprises the communication equipment comprising a processor configuredto receive the CDMA signal.
 51. The communication system of claim 48,wherein at least one communication terminal adapted for operation in thecommunication system comprises the communication equipment comprising aprocessor configured to receive the CDMA signal.
 52. The communicationsystem of claim 48, wherein at least one communication terminal adaptedfor operation in the communication system comprises the communicationequipment comprising a processor configured to receive from an inputdata to be transmitted.